Elevated CO2 Levels do not Affect the Shell Structure of the Bivalve Arctica islandica from the Western Baltic

Shells of the bivalve Arctica islandica are used to reconstruct paleo-environmental conditions (e.g. temperature) via biogeochemical proxies, i.e. biogenic components that are related closely to environmental parameters at the time of shell formation. Several studies have shown that proxies like element and isotope-ratios can be affected by shell growth and microstructure. Thus it is essential to evaluate the impact of changing environmental parameters such as high pCO₂ and consequent changes in carbonate chemistry on shell properties to validate these biogeochemical proxies for a wider range of environmental conditions. Growth experiments with Arctica islandica from the Western Baltic Sea kept under different pCO₂ levels (from 380 to 1120 µatm) indicate no affect of elevated pCO₂ on shell growth or crystal microstructure, indicating that A. islandica shows an adaptation to a wider range of pCO₂ levels than reported for other species. Accordingly, proxy information derived from A. islandica shells of this region contains no pCO₂ related bias.     

Flavonoid systematics of ten sections of Ludwigia (Onagraceae)

Data for the flavonoids of 19 species in 10 sections of Ludwigia are presented. Eight flavonoids, comprising four glycoflavones, of which vitexin and isovitexin are reported for the first time in Ludwigia, and four flavonol glycosides, based on quercetin, are present in these species. Each section treated here has either glycoflavones or flavonols; presence of only onte class is considered to be advanced in the genus as a whole, compared with the presence of both glycoflavones and flavonols in the more generalized sects Myrtocarpus Cinerascentes, and Pterocaulon, which were examined earlier. Only glycoflavones are present in sects Macrocarpon (four species), Seminuda (five species), the ditypic African sect. Africana, the monotypic African sects Brenania, Cryptosperma, and Prieurea, the monotypic east Asian sect. Nipponia, and the monotypic pantropical section Fissendocarpa. Only flavonols are present in the monotypic Old Wodd section Caryophylloidea and sect. Oligospermum, which comprises nine species widespread in the OId and New Worlds.     

Studies on the protolytic reactions coupled with water cleavage in photosystem II membrane fragments from spinach

The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 s flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H⁺-release takes place followed by a slower H⁺-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H⁺-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H⁺-uptake is observed in the subsequent flashes; c) the extent of the H⁺-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions S_i S_i+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H⁺-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q₄₀₀(Fe³⁺) formed due to dark incubation with K₃[Fe(CN)₆]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.Abbreviations A protonizable group at the PSII acceptor side - BCP Bromocresol Purple - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FWHM Full Width at Half Maximum - Q_A, Q_B primary and secondary plastoquinone at PSII acceptor side - Q₄₀₀ redox group at PSII-acceptor side (high spin Fe²⁺) - P680 Photoactive chlorophyll of PSII reaction center - S_i redox states of the catalytic site of water oxidation - Z redox component connecting the catalytic site of water oxidation with the reaction center     

Identification and sequence of the VH gene elements encoding a human anti-DNA antibody

Antibodies to DNA similar to those found in patients with systemic lupus erythematosus (SLE) and autoimmune mice can be derived from the lymphocytes of normal individuals. It is not known whether these normal derived anti-DNA antibodies are made from the same VH gene elements as the anti-DNA antibodies made by SLE patients. To begin to answer this question, we examined mu chain cDNA clones from human hybrid clone C6B2 producing anti-DNA antibodies. The sequence of the 500 base pair restriction fragment containing the variable region (5' terminus) was determined and was sequenced. This antibody uses a VHII heavy chain subgroup gene, a J3 joining segment, a hitherto unknown D segment, and a previously reported leader sequence. Significant homology was found to a mouse anti-DNA antibody sequence in the use of VH subgroup in J3, and in the hypervariable regions with a shared Ser-Tyr construction in CDR1 and an identical five amino acid residue stretch in CDR2. Comparison with the limited sequence data of published SLE monoclonal anti-DNA antibodies, both human and mouse, suggests that this shared Ser-Tyr may be important in some but not all antibodies to DNA. Comparison of C6B2 antibody is made with other known antibody sequences with identification of those residues likely to be part of the antigen binding site.     

Alternative base pairing between 5''- and 3''-terminal sequences of small subunit RNA may provide the basis of a conformational switch of the small ribosomal subunit.

The compiled sequences of small subunit ribosomal RNAs have been screened for base complementary between 5'- and 3'-terminal regions. Highly conserved complementary sequences are found which allow formation of a helix between the two ends of 5 or 6 base pairs. This helix is composed of sequences from the loop region of the first 5'-terminal stem and from sequences immediately distal to the last stem (the Me2A-stem) of the 3' terminus and therefore allows a coaxial stacking with either of these two flanking stems. Formation of the 5'/3'-helical arrangement is, however, only possible at the cost of dissolving the 'pseudo-knot' helix between the 5'-terminal region and the internal region of small subunit RNA. It is postulated that the mutually exclusive conformational states are in dynamic equilibrium and that they correlate with distinct functional states of the small ribosomal subunit. The 'pseudo-knot' containing conformation with the 3'-terminal sequences more exposed is likely to represent the initiating state, whereas the 5'/3' terminal paired 'closed' conformation may represent the elongating state in which interaction with fortuitous ribosomal binding sequences of mRNAs is avoided.     

The primary structure of the mitochondrial energy-linked nicotinamide nucleotide transhydrogenase deduced from the sequence of cDNA clones

The amino acid sequence of the bovine mitochondrial nicotinamide nucleotide transhydrogenase, which catalyzes hydride ion transfer between NAD(H) and NADP(H) coupled to proton translocation across the mitochondrial inner membrane, has been deduced from the corresponding cDNA. Two clones were isolated by screening a bovine lambda gt10 cDNA library, using two synthetic oligonucleotides and a cDNA restriction fragment as probes. The inserts together covered 3,105 base pairs of coding sequence, corresponding to 1.035 amino acid residues. However, the reading frame at the 5' end was still open. N-terminal sequence analysis of the isolated enzyme indicated the presence of 8 additional residues. Thus, the mature transhydrogenase appeared to have 1,043 amino acid residues and a calculated molecular weight of 109,212. The deduced amino acid sequence of the transhydrogenase contained the sequences of four tryptic peptides that had been isolated from the enzyme. Two of these were the peptides that had been used for construction of the oligonucleotide probes. The other two were tryptic peptides isolated after labeling the NAD-binding site of the transhydrogenase once with [3H]p-fluorosulfonylbenzoyl-5'-adenosine (FSBA), and another time with [14C]N,N'-dicyclohexylcarbodiimide. The FSBA-labeled peptide was found to be located immediately upstream of the [14C]N,N'-dicyclohexylcarbodiimide-labeled peptide, about 230 residues from the N terminus. One of the tryptic peptides used for oligonucleotide probe construction was the same as that labeled with [3H]FSBA when the NAD-binding site was protected from FSBA attack. This peptide, which might be at the NADP-binding site of the transhydrogenase, was located very near the C terminus of the enzyme. The central region of the transhydrogenase (residues 420-850) is highly hydrophobic and appears to comprise about 14 membrane-spanning segments. By comparison, the N- and the C-terminal regions of the enzyme, which contain the NAD- and the putative NADP-binding sites, respectively, are relatively hydrophilic and are probably located outside the mitochondrial inner membrane on the matrix side. There is considerable homology between the bovine enzyme and the Escherichia coli transhydrogenase (two subunits, alpha with Mr = 54,000 and beta with Mr = 48,700), whose amino acid sequence has been determined from the genes (Clarke, D.M., Loo, T.W., Gillam, S., and Bragg, P.D. (1986) Eur. J. Biochem. 158, 647-653).     

A method for determining overall protein fold from NMR distance restraints

Summary We describe a simple method for determining the overall fold of a polypeptide chain from NOE-derived distance restraints. The method uses a reduced representation consisting of two particles per residue, and a force field containing pseudo-bond and pseudo-angle terms, an electrostatic term, but no van der Waals or hard shell repulsive terms. The method is fast and robust, requiring relatively few distance restraints to approximate the correct fold, and the correct mirror image is readily determined. The method is easily implemented using commercially available molecular modeling software.     

Ferritin enhances production of DNA strand breaks by 6-hydroxydopamine,ascorbic acid and H2O2 in CCC PM2 bacteriophage DNA

Damage of CCC PM2 DNA by 6-hydroxydopamine (6-OHDA) and ascorbic acid (AA), compounds that are both able to release iron from ferritin, was significantly enhanced in the presence of ferritin. H₂O₂, a product of 6-OHDA autoxidation, did not induce DNA strand breaks in the absence of ferritin and only to a minor extent in the presence of ferritin. DNA damage by 6-OHDA and AA could be reduced by the hydroxyl radical scavenger mannitol, the iron chelator desferrioxamine, and, partly, by a combination of superoxide dismutase and catalase. These inhibitory effects were clearly less pronounced in the presence of ferritin. Ferritin obviously played an important role as a source of iron in the pro-oxidative processes of 6-OHDA and AA. These features might be of importance in cancer therapy since many tumor cells contain elevated ferritin levels.